The invention relates to a method of preparing diene polymers having a high content of cis-1,4 addition along with good green strength and tack. More particularly, the invention relates to a method of preparing such polymers which involves polymerizing a 1,3-diene monomer in solution in the presence of a novel catalyst system which comprises a carboxylated metal oxy borate compound in which the metal is nickel or cobalt, an organometallic compound of a metal of Groups I, II, and III and one or more fluorine containing compounds.
Polybutadiene polymers having a high content of cis-1,4 addition and methods for their preparation are known in the art. Such polymers have been produced by polymerizing 1,3-butadiene under solution polymerization conditions using a wide variety of catalyst systems including catalyst compositions composed of various organonickel or organocobalt compounds, organometallic compounds of metals of Groups I, II, and III and various fluorine containing compounds.
Thus, U.S. Pat. No. 3,483,177 to Throckmorton, et al. relates to a method of preparing polybutadienes having a high content of cis-1,4 addition which comprises polymerizing 1,3-butadiene in solution in the presence of a catalyst system consisting of a mixture of: (1) organometallic compounds of the metals of Groups I, II, and III, including among which is disclosed trialkyl aluminum compounds; (2) at least one compound selected from the class consisting of organonickel or organocobalt compounds; and (3) at least one boron trifluoride complex prepared by complexing boron trifluoride with at least one member of the class selected from ketones, aldehydes, esters and nitriles, all members of the class having a carbon atom attached directly by a multiple bond to at least one atom selected from oxygen and nitrogen. At column 2, lines 13-21, there is described a prior art catalyst composition comprising triethyl aluminum, an organonickel salt and a boron trifluoride-diethyl ether complex.
U.S. Pat. No. 3,528,957 to Throckmorton, et al. relates to a method of preparing polybutadienes having a high content of cis-1,4 addition which comprises polymerizing 1,3-butadiene in solution in the presence of a catalyst system consisting of a mixture of: (1) organometallic compounds of metals of Groups, I, II, and III; (2) at least one compound selected from the class consisting of organonickel and organocobalt compounds; and (3) at least one boron trifluoride complex prepared by complexing boron trifluoride with a member of the class consisting of monohydric alcohols, phenols, water and mineral acids containing oxygen.
U.S. Pat. No. 3,985,941 to Pierson, et al. relates to a method of preparing polybutadienes having a high content of cis 1,4 addition which comprises polymerizing 1,3-butadiene in solution in the presence of a catalyst system consiting essentially of: (1) an organoaluminum compound selected from the group consisting of triisobutyl aluminum and tri-n-butyl aluminum; (2) an organonickel compound; and (3) a fluorinated mixture of hydrogen fluoride etherate and boron trifluoride etherate.
U.S. Pat. No. 4,304,885 to Omori, et al. relates to a polybutadiene rubber composition having high tack in the unvulcanized state which comprises a blend of a normally solid polybutadiene of high molecular weight with an extremely soft low molecular weight polybutadiene polymer. The patent discloses that both polymers are prepared by solution polymerization using various catalyst systems including catalyst systems consisting of organonickel compounds, trialkyl aluminum compounds and boron trifluoride etherates.
The aforementioned patents describe methods of preparing polybutadienes having high contents of cis-1,4 addition utilizing polymerization catalyst systems bearing some similarities to the catalyst systems employed in the method of the present invention.
However, there are a number of very important distinctions between the catalyst systems employed in the processes of this prior art and the catalyst systems used in the method of the invention which affect both the nature of the polymerization and the properties of the resultant polybutadiene polymers. Thus, none of the above mentioned patents disclose or suggest that the polybutadiene polymers produced by the methods described therein exhibit both good green strength and tack. In fact, as pointed out in U.S. Pat. No. 4,242,232, one of the major disadvantages of high cis-1,4 polybutadiene polymers produced by catalyst compositions of the prior art which utilize transition metals such as titaium, cobalt, and nickel, is inferior tack as compared to natural rubber.
U.S. Pat. No. 4,304,885 does teach that the polybutadiene rubber compositions described therein have high tack. However, in accordance with the teachings of the patent, this high tack property is achieved by blending a high molecular weight polybutadiene with a low molecular weight polybutadiene and this appears to be the case even though the reference recommends the use of catalyst systems for preparing the polymers which are at least analogous to those described in the above patents.
Moreover, U.S. Pat. Nos. 3,483,177; 3,528,957; and 3,985,941 all clearly teach that when certain boron trifluoride complexes, such as, for example, boron trifluoride etherates are employed in the catalyst system and the organometallic compound employed is a trialkyl aluminum compound, the selection of the trialkyl aluminum component is extremely limited. Thus, these patents all teach that in such instances the trialkyl aluminum compound should be limited to triethyl aluminum or trimethyl aluminum if optimum reaction rates and polymer molecular weights are to be obtained. This is in complete contrast to the catalyst composition of the present invention in which the trialkyl aluminum component is not so limited.
Finally, the organonickel or organocobalt components of the catalyst systems of the aforementioned prior art patents are entirely different from the carboxylated metal oxy borate component of the catalyst system of the present invention. As will be discussed hereinafter, this component of applicants' catalyst system is of major significance in producing polybutadienes having both a high content of cis-1,4 addition and good green strength and tack.